Had Jason Bay re-signed with the Red Sox, the deal likely would have been heralded. The idea that a slugger who seemed to fit perfectly into the Red Sox lineup, ballpark and clubhouse had come to an agreement to return made enormous sense. Through most of 2009, the industry-wide expectation was that the outfielder would be back.

But when that turned out not to be the case, and Bay instead landed with the Mets, the reaction was far less enthusiastic. Suggestions in the aftermath of the four-year, $66 million deal that includes a vesting option that can push the deal to approximately $80 million over five years are widespread that a) the Mets had failed to address their most significant deficiency, b) Bay had no interest in going to the Mets, and only went because no other legitimate options existed, and c) Citi Field is a park that is death to homers and demands defense for the expansive left field, thus diminishing one of Bay’s foremost assets (power) and accentuating one of his chief liabilities (defense).

A few thoughts on each:

–At the start of the offseason, multiple rival executives believed that the Mets wouldn’t get in the bidding for Bay due to their acute need for pitching. And when the Mets arrived at the Winter Meetings, they didn’t necessarily disagree. But New York looked at a landscape in which the top pitcher (John Lackey) was going to command a larger contract than Bay both in years and dollars.

The other free-agent pitchers — hurlers along the lines of Joel Pineiro and Jason Marquis, among others — were looking for the types of commitments that made the gap in annual salary between them and the top-of-the-market players (Bay, Lackey, Matt Holliday) relatively negligible considering the difference in impact.

Given that the health of pitchers in their 30s over a four- or five-year deal is almost always a riskier proposition than that of hitters, and that negotiations for Holliday (with agent Scott Boras) seemed likely to be protracted and filled with demands for Mark Teixeira-type money, Bay represented, to the Mets, a superior balance of risk, impact and investment size.

Even so, the Mets were under no illusions that their pitching staff is without flaws. That said, adding another pitcher would only do so much to boost a staff that has one front-line pitcher (Johan Santana) and a bunch of question marks. Adding a slugger — especially one who with the ability to produce at Citi Field (more on that in a bit) — offered the possibility of transforming the Mets offense from decent (assuming that Jose Reyes returns and approximates his prior career performance) to elite. And the Mets arguably had more room to upgrade their lineup of 2009 than they did their run prevention, since New York scored 671 runs last year, 12th among the 16 N.L. teams. By contrast, the team’s pitching permitted 757 runs, a mark that ranked ninth.

The team felt it looked better with Bay in the lineup than with Lackey in the rotation. And while there is risk on the pitching staff, there have been other recent seasons when the current pitching group has been above average: in 2008, for instance, Santana was brilliant (2.53 ERA), while Mike Pelfrey (3.72), Oliver Perez (4.22) and John Maine (4.18) all had an above-average ERA+. There is no doubt that there are significant question marks looming over Pelfrey, Perez and Maine going forward. But there is also a chance that the trio could be adequate to put the Mets in position where a significant jump in offense (with healthy seasons from Reyes and Carlos Beltran) could be enough to help the team improve significantly.

–The notion that Bay had no — or even limited — interest in the Mets was inaccurate, according to a source familiar with the negotiations. There is little question that Bay’s agent, Joe Urbon, tried to engage other clubs, but that is a common practice in free agency. According to the same source, when the Mets presented their offer, they received assurances of Bay’s interest in going to the team, and the two sides remained in near constant dialogue until an agreement was reached. The suggestion that the two sides experienced a lengthy period of non-contact while Urbon contacted other clubs was inaccurate, with there having been just one day when the two sides were not in contact.

Once the Mets broke the four-year threshold of the Sox’ offer by offering Bay a vesting option for a fifth year, it was reasonable for Bay to see if he could find a contract that included a fifth guaranteed year. Had that happened, the Mets might well have sweetened their offer to include a guaranteed fifth year. But, since there was no evidence of an offer by any other club for more than four years, and since Bay had rejected the Red Sox offer, the Mets could hold to the original framework that they proposed, and finalize the deal by a slight improvement in the guaranteed money and making the vesting option more attractive. (Contrary to some reports, the Mets never offered a deal that featured a guaranteed fifth year.)

And, in some ways, it is only appropriate that Bay would get an extra year based on a vesting option that is dependent on his health. After all, Urbon made the case to clubs that Bay was the durable and productive outfielder on the market. If he is confident of retaining that status, then he should feel confident in achieving the terms of the vesting option.

–As for the Citi Field impact on Bay, time will tell. It may be somewhat premature to characterize the park solely on the basis of its one-year existence.

That said, the Mets found that while the park plays big to the alleys and centerfield, that it is generous to right-handed pull power. The first year at Citi Field featured 10 percent more homers to left field than the average park, according to a source. Bay hit 22 of his 36 homers to left in 2009, another dozen to center and just two to the opposite field.

And, Bay’s power was anything but a byproduct of Fenway Park. Of his 36 homers in 2009, 21 of them came on the road.

While David Wright became a posterboy for the notion that the cavernous Citi Field was death to right-handed power hitters thanks to a precipitous drop from 33 homers in 2008 to 10 in 1009, his first in his new home park, the park does not account for the fact that Wright’s road homer total fell from 12 in 2008 to five in 2009. In many respects, it appears that Wright, in an otherwise strong year (.307 average, .390 OBP), did not drive the ball in a manner consistent with his past performance.

In Bay, the Mets have acquired a player whom they believe can sustain his power numbers in their new park. As for criticisms about Bay’s defense, the Mets believe that they have been exaggerated. Fenway Park, of course, skews the defensive metrics of left fielders. Bay is likely a slightly below average defender in left, but not so poor that his glove would offset his considerable offensive production. If it did, one can bet that the Sox — who believe strongly in defensive metrics, as evidenced by this offseason’s overhaul — wouldn’t have put a four-year, $60 million offer on the table.

–In the end, the Mets decided that Bay represented the safest value-for-dollar player on the high-end of the free-agent scale. Bay, meanwhile, received a contract that includes a guarantee that was 10 percent higher (in total unadjusted dollars) than the last offer made by the Sox, and that includes the possibility of an extra year. Ultimately, that positioned the two sides to reach an agreement.

The wisdom of the deal will be tested over the coming four or five years, but at least initially, the fit between the player and his new club is probably better than what has been characterized. Bay is a player who has managed to thrive regardless of setting, who has adapted well to change throughout his career and who seems to enjoy playing in a charged atmosphere of a major market after years spent in baseball obscurity. The Mets acquired a player who should be able to handle the critical environment and whose game, they believe, will translate well to their park and team.